An integrated gasification combined cycle (IGCC) complex converts fossil fuel to power and hydrogen (H2). IGCC complexes include a gasification step, an acid gas removal section, a power generation section, and hydrogen recovery units. The fossil fuels are fed to a gasifier in the gasification step. Fossil fuels fed to gasifier can include coal, vacuum resid (VR), and high sulfur fuel oil (HSFO).
In gasifiers, the fossil fuel feed is reacted with pure oxygen and steam to produce syngas at an elevated temperature and pressure. Syngas from the gasifiers is then sent to the acid gas removal (AGR) section for removal of acidic gases such as hydrogen sulfide (H2S) and carbon dioxide (CO2). One common AGR process includes a hydrolysis reactor to convert carbonyl sulfide (COS) to H2S and CO2. The H2S and CO2 are fed to an acid gas absorber to remove the H2S and at least a portion of the CO2 from the stream. Part of the effluent from the AGR process is sent to a power generation system to produce electricity, and the remainder is sent to a hydrogen recovery unit (HRU) to recover and produce H2. The power generation section typically uses a combustion turbine to generate electricity.
In addition to acid gases, the syngas contains ppm levels of nickel carbonyl (Ni(CO)4) (Ni-carbonyl) and iron pentacarbonyl (Fe(CO)5) (Fe-carbonyl). Ni-carbonyl and Fe-carbonyl are toxic and pose significant risks to health and the environment. In addition, carbonyls in the syngas can be deposited in the gas turbine during combustion. The deposition of carbonyls decreases the efficiency of the performance of the gas turbines. Therefore, some IGCC systems include a carbonyl treatment step upstream of the gas turbines.
Commonly, the carbonyl treatment bed upstream of the gas turbines includes an activated carbon bed (ACB). The syngas stream is passed through the ACB to remove carbonyls before being combusted in the gas turbine to generate power. The carbonyls are adsorbed on the activated carbon. The spent carbon, with carbonyls adsorbed, is then burned in a kiln to eliminate the adsorbed carbonyls.
The activated carbon in an ACB requires replacement every few months, depending on the carbonyl content in the feed, in a labor intensive replacement process. The process to remove adsorbed carbonyls provides a potential point at which carbonyls can be released into the atmosphere, making even the removal process hazardous.
In other methods, sacrificial metals are used to remove the carbonyls in the carbonyl treatment step. Sacrificial metals, such as ZnS, cannot be regenerated and must be discarded. The disposal of the sacrificial metals poses significant safety risks.
Therefore, a process that reduces the risk of carbonyls to the gas turbine and reduces the risks due to carbonyl exposure is desired.